Journal of Manufacturing Processes 66 (2021) 269–280
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Journal of Manufacturing Processes
journal homepage: www.elsevier.com/locate/manpro
Investigation for macro mechanical behavior explicitly for thin-walled parts
of AlSi10Mg alloy using selective laser melting technique
Yingfeng Zhang a, *, Arfan Majeed a, Muhammad Muzamil b, Jingxiang Lv c, Tao Peng d,
Vivek Patel e
a
Key Laboratory of Industrial Engineering and Intelligent Manufacturing, Ministry of Industry and Information Technology, School of Mechanical Engineering,
Northwestern Polytechnical University, Shaanxi, China
Mechanical Engineering Department, NED University of Engineering and Technology, Karachi, 75270, Pakistan
c
Key Laboratory of Road Construction Technology and Equipment, Ministry of Education, School of Construction Machinery, Chang’an University, Xi’an, 710064,
Shaanxi, China
d
Key Laboratory of 3D Printing Process and Equipment of Zhejiang Province, Institute of Industrial Engineering, School of Mechanical Engineering, Zhejiang University,
Hangzhou, 310027, China
e
School of Materials Science and Engineering, Northwestern Polytechnical University, Shaanxi, China
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Selective laser melting
Relative density
Mechanical properties
Thin-walled specimens
AlSi10Mg
Wall thickness
Recently additive manufacturing of aluminum alloys by selective laser melting (SLM) is of research interest due
to its potential benefits in manufacturing industries. The present work investigates the SLM-built AlSi10Mg thinwalled parts and their macro-mechanical behavior in correlation with relative densities. The superlative me­
chanical behavior of SLM parts was achieved by using the optimal parameters, i.e. 320 W of laser power, 900
mm/s of scanning speed, and 80 μm of hatch distance. The results showed that the SLMed AlSi10Mg thin-walled
specimens attained the highest relative density of 99.86 % and 99.21 % for the wall thickness of 0.50 mm and 5.0
mm, respectively. For 0.50 mm wall thickness specimen, the tensile strength of 250.9 MPa, yield strength of
143.7 MPa, breakage elongation of 5.31 %, and microhardness of 116.8 HV were attained which would be
comparable to those of the conventionally die-cast A360 alloy. The 364 MPa of tensile strength and 12.04 % of
breakage were achieved for 5.0 mm thin-walled specimen. The fracture behavior of different thin-walled
fabricated tensile specimens was also examined using a scanning electron microscope (SEM).
1. Introduction
Selective laser melting (SLM) is a relatively mature additive
manufacturing (AM) technology, which allows the manufacturing of
lightweight, thin-walled, honey-comb, or porous structured parts, con­
forming good mechanical properties without using object-specific tool­
ing or downstream sintering processes [1]. The development of the SLM
process has turned it to generate custom-made single parts that are
difficult to produce by the conventional approaches, consisting of each
part in a unique and novel manner in the batch. The basic principle of
SLM is to fabricate a geometric model (3D model generated by
computer-aided design) using a layer-by-layer approach. SLM can
manufacture the products from loose powder that not only an acceptable
physical shape but also have similar mechanical properties [2].
At present, SLM for lightweight materials is concentrated on titanium
alloys [3], steel and iron-based alloys [4], nickel alloys [5], and
aluminum alloys [6]. Among them, aluminum alloys are of great
research interests because of its potential benefits. The Al-Si alloys are
the most commonly studied Aluminum alloys, which are categorized as
the casting aluminum alloys [7], and they are mainly applied due to
their excellent weldability, high hardness and strength, high fluidity,
low coefficient of thermal expansion, and excellent corrosion resistance
[8]. Al-Si-Mg alloys are conventionally used in the fabricating of
thin-walled and lightweight casting products having complex geomet­
rical features subjected to higher loading conditions [9]. During the SLM
process, the interaction between the concentrated laser beam and the
loose powders leads to an immensely higher-temperature gradient with
very high-level heating, melting, and cooling rates [10]. AlSi10Mg alloy
has been widely investigated, and it is similar to the A360 casting alloy
[11].
* Corresponding author.
E-mail addresses: zhangyf@nwpu.edu.cn (Y. Zhang), amajeed@mail.nwpu.edu.cn (A. Majeed), muzamil@neduet.edu.pk (M. Muzamil).
https://doi.org/10.1016/j.jmapro.2021.04.022
Received 9 April 2019; Received in revised form 8 February 2021; Accepted 3 April 2021
1526-6125/© 2021 Published by Elsevier Ltd on behalf of The Society of Manufacturing Engineers.
Y. Zhang et al.
Journal of Manufacturing Processes 66 (2021) 269–280
SLM allows direct fabrication of lattice and light-weight structures
with gradual and controlled porosity. Thin-walled parts are broadly used
in several products of aerospace, automobile, power engineering, avia­
tion, etc., where lightweight, high usability, and ergonomics are the key
aspects [12,13]. Thin-walled or lattice structures manufacturing char­
acterizes a sole problem in the determination of mechanical properties.
Ben et al. [14] investigated the influence of reducing wall thickness on
the mechanical properties of SLM built samples of SS-304 L and EBM
built samples of Ti-6Al-4 V and proposed the threshold between the bulk
and thin-walled structures mechanical properties for SS-304 L and
Ti6Al4V. They also reported that the mechanical properties would be
changed by changes in the wall thickness and higher mechanical prop­
erties were found in large wall thickness specimens. Algardh et al. [15]
investigated the thin-walled parts of Ti6Al4V fabricated by the EBM
process and found that optimization of the mechanical properties of
thin-walled components can be achieved by careful process control in
terms of melting strategy and build layer thickness.
Limited literature is available highlighting the relationship between
the process parameters and mechanical properties of thin-walled
structures of aluminum alloys (or AlSi10Mg alloy) towards achieving
fully dense parts using SLM. Ahuja et al. [16] explored the impact of
laser power, scan speed, exposure time, and hatch distance on the
relative density of fabricated thin-walled structures of Al-2219 and
Al-2618 by using the SLM approach, and proposed that support struc­
tures have performed an essential effect on the porosity and cracks in the
fabricated test specimens. Recently, Qiu et al. [17] investigated
AlSi10Mg cellular lattice structures, which were fabricated by SLM at
various scan speeds and laser powers, and reported the relationship of
laser process parameters on the resulting fabricated part’s porosity and
geometry. Calignano et al. [18] performed tests to investigate the in­
fluence of processing parameters for the manufacturing of thin walls for
AlSi10Mg alloy by using the laser powder bed fusion (LBBF) and
developed a mathematical model, which were compared with the
as-designed and as-manufactured thin walls.
Apart from the importance of process parameters, different and
unique sort of experimentations and analysis have also been hit on the
AlSi10Mg alloy in the direction of laser melting. Park et al. [19] studied
the growth morphology of AlSi10Mg alloy during the solidification
process and ultimately the developed microstructure against the pa­
rameters is responsible for the built layer parts. Subbiah et al. [20] has
also drafted their investigations on AlSi10Mg alloy against a series of
process parameters to highlight the superiority of SLM technology over
the others. The fabricated structure exhibits higher mechanical strength
but depicts reduction in %elongation due to the porosities and unmelted
powder. So, the researchers suggested and enrooted toward the post
heat-treatment operation for the previously stated problem.
The progress has been made in the field of SLM for fabricating
different ferrous and non-ferrous alloys. However, there is a lot of
research gap in the implementation of SLM for the manufacturing of
thin-walled parts of AlSi10Mg alloy, which includes wall-thickness in­
fluences on the densification and mechanical properties. The present
work aims to evaluate the effect of wall-thickness on the performance of
SLM AlSi10Mg parts that includes relative density, tensile strength, yield
strength, elongation, and hardness against the parameters (laser power,
scan speed, hatch space, and layer thickness) as given in Table 1. The
expected innovation and novelty lies within the need to develop a
suitable criteria (variation in mechanical behavior) for the successful
manufacturing of full dense conditions for AlSi10Mg thin-walled parts
using SLM, since the available studies so far were only reported the bulk
component behavior. Moreover, this research work directs towards the
considerations of wall thickness as design factor, like other parameters
mentioned above, in the performance of functional or operational parts
for SLM. In this study, a comprehensive range of thin-walled thickness
were selected (that are 0.5 mm, 0.8 mm, 1 mm, 1.15 mm, 1.5 mm, 18
mm, 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, and 5 mm) to provide a
strong and healthier correlation of macro-mechanical behavior.
2. Experimental methodology
2.1. SLM process
SLM was selected as the AM process to manufacture thin-walled
specimens. The method of fabricating a part by SLM is demonstrated
in Fig. 1. Firstly, the 3D-CAD file is converted to sliced-layers form and
then transferred to the machine. Secondly, the build plate is heated
(temperature is material dependent). Thirdly, a layer of powder from the
powder feeder with a pre-defined layer thickness is spread over the
heated build plate by wiper blades. The uniformity of the deposited layer
is critical to prevent it from the defects or porosities [21]. Fourthly, a
laser beam focused onto the powder-bed is carried through an optical
fiber and radiated onto the powder layer. The laser beam selectively
melts the regions of interest on the currently deposited powder layer.
The information attached to each layer is used to guide the laser beam
across the powder-bed. Additionally, the piston-controlled build plate is
moved downward a distance equal to the predefined layer thickness to
allow the deposition of another layer of powder.
Furthermore, the sequence is then repeated several times equal to the
number of slices the part has been divided into until the full part is built
layer-by-layer [22]. Each scan penetrates deeper than the powder layer
thickness leading to the metallurgical bonding of one layer to another
[23].
2.2. The experimental setup and material
For the present work, the SLM 280HL facility is utilized to manu­
facture test specimens. The SLM machine is equipped with 02 fiber lasers
of the maximum power of 400 W with a maximum scan speed of 10,000
mm/s and a focal laser beam diameter of 80 μm. A square building
platform of 280 × 280 mm in dimension with 365 mm in height is used
to build test specimens. To prevent the oxidization of the AlSi10Mg
powder during the SLM process, the argon gas was fed inside the ma­
chine chamber at the pressure of 11.5–12.5 mbar, thereby decreasing
the oxygen level below 0.1 %. The 3A21 aluminum substrate was heated
to 150 ◦ C to avoid the thermal stresses and deformation of the manu­
factured parts due to the uneven distribution of temperature. AlSi10Mg
in gas-atomized form was used as powder material for making
Table 1
Optimized process parameters for the ASi10Mg alloy from previous literature and the present study.
Laser Power
(W)
Scan Speed (mm/
s)
Hatch space
(μm)
Layer Thickness
(μm)
Relative Density
(%)
AM Equipment
References
200
250
1200
500
105
150
30
50
99.10
>99.0
175
100
350
350
320
1035
500
1140
1600
900
150
50
170
130
80
30
40
50
30
30
>99.0
99.77
99.8
99.13
93.6− 99.86
Concept Laser M1 SLM machine
Trumpf TrumaForm LF130 powder-bed
machine
Concept Laser M2 Cusing SLM system
Realizer GmbH SLM-50
SLM 250 H L machine
SLM 125 H L (SLM Solutions)
SLM 280 H L
Kempen, Lore [27]
Brandl, Heckenberger
[28]
Read, Wang [11]
Aboulkhair, Everitt [29]
Yap, Chua [30]
Raus, Wahab [31]
Present study
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Journal of Manufacturing Processes 66 (2021) 269–280
Fig. 1. SLM process schematic presentation.
specimens that were supplied by powder alloy corporation (PAC), USA.
samples in the range of 6− 10 mm have been manufactured to obtain
tensile specimens for testing, but in the present study, the wall thickness
is changing for each test specimen such as 0.50–5.0 mm. For each
combination of parameters, two rectangular samples for tensile testing
with a dimension of 56 mm × 10.5 mm x Wt were formed, where Wt is
the wall thickness of specimens. Two bulk samples with a dimension of 8
× 6 × 10 mm were also manufactured for investigating the effect of
process parameters on the densification and hardness which are shown
in the top right side of Fig. 2a.
A total of 24 numbers (02 sets) rectangular thin-walled specimens
were produced to make tensile specimens (see Fig. 2a). The building
direction of the test specimen is in the vertical direction along the Z-axis
which is shown in Fig. 2b. A checkerboard scanning strategy was chosen
to minimize residual stresses during the fabrication of test specimens
[32]. For one specific powder layer, the checkerboard is scanning line­
arly, and the linear scanning direction rotates with 67◦ for the next
powder layers, as shown in Fig. 2c. The samples were cut from the
substrate by wire cutting machine. The tensile test specimens were
produced according to E8/E8M subscale as shown in Fig. 3 [33].
2.3. The processing parameters
The selection of appropriate process parameters is based on the op­
tical, thermal, and mechanical phenomena stimulated during the laser
beam matter interaction [24]. Different researchers have used different
process parameters for the manufacture of AlSi10Mg parts and opti­
mized the main process parameters such as scan speed, laser power,
hatch distance, and slice thickness for achieving maximum relative
density, mechanical properties, hardness, and defect-free microstruc­
ture. The above mentioned four parameters have a significant influence,
and their combined effect is known as the energy density (ED) [25]. The
ED is described as Eq. (1):
ED =
PL
(Vs × hd × tL )
(1)
Based on energy density, the researchers have optimized processing
parameters which are mentioned in Table 1. In this study, we have also
obtained the optimal processing parameters with first-hand experiments
[26], which are also mentioned in Table 1. Usually, the thick-walled
Fig. 2. a) The rectangular thin-walled and cubic bulk samples, b) Building orientation in the vertical z-axis direction, and c) Checkerboard scanning strategy
with 67◦ .
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Journal of Manufacturing Processes 66 (2021) 269–280
Fig. 3. E8M subscale samples for tensile strength testing.
2.4. Powder characterization
paper.
The gas-atomized AlSi10Mg powder characteristics were examined
and its chemical composition is presented in Table 2. Analysis of the asreceived gas-atomized AlSi10Mg alloy powder revealed that more than
78 % of the evaluated particles have the size in the range of 10–63 μm, as
shown in Fig. 4. Based on the SEM observations in Fig. 5, the
morphology of the powder particles is a combination of spherical and
elongated elliptical shapes, and some large particles contain small par­
ticles within them. The small particles contribute to the high energy
absorption of the laser beam because of the increased specific surface
area of material [34]. The spherical morphology of powder provides
good flowability and consistent layer distribution. Bigger bunches of
length larger than 60 μm were also detected. Prior to the SLM process,
the powder was dried in a vacuum furnace at 70 ◦ C for 4 h and then
sieved in an inert atmosphere to isolate particles between 15 μm–58 μm.
2.6. The responses and their measurements
The particle morphology of the AlSi10Mg powder was measured by
Tescan VEGA 3 LMU scanning electron microscope (SEM), an average
particle size distribution was measured by using an LS particle size
analyzer of Beckman Coulter LS 13 320. Relative density was calculated
by applying Archimedes’ principle [36] which was measured by the
density of the fabricated test specimen to the density of bulk material
that is 2.68 g/cm3 for AlSi10Mg [37]. The micrographs of test specimens
were examined with an optical inverted metallurgical microscope
(Olympus GX-71) with a built-in front camera port and fracture surfaces
were examined by Tescan VEGA 3 LMU SEM system.
The thin-walled and bulk samples were mechanically ground on SiC
abrasive papers of various grits, followed by polishing with diamond
pastes of 5 μm to 0.5 μm. Tensile testing was performed on each thinwalled test specimen to evaluate ultimate tensile strength (UTS), yield
strength, and breakage elongation. A universal Instron-3381 equipped
with 100 kN load cell and extensometer was used for tensile testing of
test specimens at room temperature, and a crosshead speed of 0.50 mm/
min was used. Microhardness measurements were performed on a LECO
AMH 43 automatic hardness tester under a load of 50 gm and dwell time
of 10 s. The mean value of 10 measurements of each specimen is taken.
2.5. Thin-walled specimens manufacturing
Two sets of thin-walled specimens were manufactured to ensure
uniformity and reproducibility of the SLM process which is shown in
Fig. 2a. The wall thickness of fabricated thin-walled test specimens was
measured at different locations, and the variations in wall thickness
from the model designed value to actual fabricated value are shown in
Fig. 6 with an error bar. It was observed that the deviations in the wall
thickness are less for 0.5, 0.8, and 5.0 mm thickness specimens. The
maximum deviation of 5.5 % is found for 1.0 mm thin-walled specimen
and the minimum variance of 0.25 % in the 0.80 mm wall thickness. The
deviations in the wall thickness are created due to high thermal stresses
and material shrinkage during the deposition process. For smaller wall
thickness, laser contact is generally less, so that laser interaction be­
comes too short with each other, resulting less amount of melting and
solidification during each layer. On the other side, when the interaction
of the laser beam is more with the built part, there are more chances of
shrinkage during the solidification process of SLM. The deviations in the
wall thickness are very low for very thin geometries, though it becomes
crucial for designing the final functional part that needs very tight
tolerance. For achieving the best accuracy during the manufacturing of
thin-walled parts, the processing parameters in relevance to beam
compensation can be modified [35]. The surface roughness of
thin-walled specimens also varied with variation in the wall thickness
and max. The surface roughness of 8.088 μm was observed in 2.5 mm
specimen. Surface roughness may be discussed in detail in a separate
3. Results and discussion
3.1. Microscopic images examination and analysis
The optical micrographs of thin-walled specimens at the top and
lateral positions are shown in Figs. 7-11. The porosities, voids, oxides
particles, and un-melted powder particles of different sizes have been
observed at different places on the top and lateral surfaces of specimens.
The pores are generally developed due to insufficient melting of powder
particles and gas entrapping. So, some spherical pores (see in Figs. 7-11)
are built due to the trapping of gas in the melt pool during rapid melting
and solidification [38]. The oxides particles are also developed in the
aluminum parts during the SLM process, irrespective of an argon at­
mosphere. Louvis et al. [22] also mentioned about the presence of
aluminum oxides during the fabrication of aluminum alloys components
by the SLM process that produced fully dense components and
concluded that high power laser would be used to break the oxide layer
on the deposited tracks. In the present study, the best optimal
Table 2
Chemical compositions of AlSi10Mg alloy powder.
Elements
Si
Mg
Fe
Ni
Cu
Ti
Zn
Mn
Sn
Pb
Al
% Weight
10.1
0.30
0.11
<0.05
<0.01
0.01
<0.01
<0.02
<0.05
<0.01
Bal
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Journal of Manufacturing Processes 66 (2021) 269–280
Fig. 4. The powder particle size distribution of AlSi10Mg powder.
Fig. 7. Microscopic images of the top surface of the 0.50 mm wall thick­
ness specimen.
Fig. 5. The morphology of the AlSi10Mg powder by SEM.
manufacture thin-walled specimens.
The top surface optical micrographs of the 0.50 mm wall thickness
(see Fig. 7) are showing the porosities of different sizes from 10 ~ 50 μm.
More porosities were observed for the 1.50 mm specimen than the 0.50
mm specimen (see Fig. 8a), and the size of the porosities are in the range
of 10–70 μm (see Fig. 8b). The microscopic images of the 2.50, 3.50, 4.0,
and 5.0-mm wall thickness specimens were also analyzed (see Figs. 8c,
d, 9). The porosities decrease with the increment in the wall thickness
due to appropriate melting and solidification of the powder particles,
full penetration of laser beam in the powder, and developing of fine
bonding of the particles and grains. In the thin-walled specimens, there
was a short time for the melting and solidification of the powder par­
ticles. As highlighted in Fig. 8a, massive pockets of porosities were
captured and highlighted at different places for 1.50 mm wall-thickness
that is further magnified in Fig. 8b for clear depiction. However, when
the wall thickness is increased from 1.50 mm to 2.5 mm, the porosities
are significantly reduced due to sufficient bonding of powder particles
that reduced the pores development and gas entrapping. Strong correl­
ative microstructures for justification are presented in Fig. 8(c–d) for 2.5
mm in contrast to 1.5 mm thickness in Fig. 8 (a–b). In addition, an
overall improved surfaces in terms of reduced porosities are presented in
Fig. 9 (a–c) for 3.5 mm, 4 mm, and 5 mm thickness comparably with
Fig. 6. Graph of the designed wall thickness to the actual measured
wall thickness.
parameters especially the high-power laser of 320 W is used to
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Journal of Manufacturing Processes 66 (2021) 269–280
Fig. 8. Micrographs of. (a-b) 1.50 mm specimen; (c-d) 2.50 mm specimen.
Fig. 9. OM images of thin-walled specimens. a) 3.50 mm; b) 4.0 mm; and c) 5.0 mm.
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Journal of Manufacturing Processes 66 (2021) 269–280
Fig. 10. Microscopic images of the lateral face; (a-b) 0.50 mm specimen; (c-d) 1.50 mm specimen.
Fig. 8 for 1.5 mm and 2.5 mm thickness.
Figs. 10,11 show the microscopic images of the lateral surface of
thin-walled specimens at various fabricated wall thickness. Lateral sur­
face OM images of the 0.50 mm wall thickness are shown in Fig. 10.
From Fig. 10b, it is clear that the size of porosities is less than 40 μm, and
the porosities appear at the molten pool or joint of two layers (layer
thickness). Also, two porosities are combined to make a collective larger
porosity which can be seen from Fig. 10a and the overall amount of
porosities is very scarce. It can be observed in Fig. 10c and d that a lot of
porosities having a size of greater than 50 μm in many positions. Fig. 11
presents the micrographic images of the 2.50 mm wall thickness spec­
imen which reveals fewer porosities less than 50 μm size. Furthermore,
some porosities are found smaller in size in comparison to the 1.50 mm
specimen. The porosities are reduced with the increment in the wall
thickness which can be observed in 3.50 mm wall thickness specimen
(see Fig. 11c and d) and 5.0 mm thick specimen (see Fig. 11e and f).
From the OM observations of the lateral surface of the thin-walled
specimens, the quantity and size of porosities and voids are smaller
for thick specimens (greater than 1.50 mm wall thickness).
mm–3.0 mm specimens, respectively, and then a gradual increment of 1
% in relative density is observed from 3.0 to 3.50 mm specimens (see
Fig. 12).
The relative density gradually increased and reached a maximum
value of 99.21 % for the 5.0 mm wall thickness specimen (see Fig. 12).
Results show that the relative density decreases from the 0.50 mm to
1.50 mm wall thickness, and the values of the relative density increase
gradually from the 1.80 mm to 5.0 mm wall thickness specimens. Usu­
ally the change in relative density values occurred due to the melting
and cooling behavior of the powder particles during the fabrication of
SLM products, and this variations further depicted in the form of po­
rosities and oxides particles in the fabricated specimens. Furthermore,
when the obtained relative densities were compared and analyzed with
the optical micrograph images (see Figs. 7-11), it is well understood that
the low-density specimens have more porosities, voids, and oxides
particles than the higher-density specimens. Here, it is worth noting that
the present study is carried out to find the density of the thin-walled
specimens of AlSi10Mg alloy in as-built condition at various wall
thicknesses.
3.2. Relative density computation
3.3. Mechanical properties and fracture surfaces behavior
The AlSi10Mg thin-walled specimens were built with the best density
and the relative density with varying wall thickness is shown in Fig. 1.
The highest relative density of 99.86 % was achieved in the 0.50 mm test
specimen. Then, the relative density was decreased gradually from
99.86 % to 93.60 % as the wall thickness increase from 0.50 mm to 1.50
mm. From the 1.50 mm to 1.80 mm wall thickness, there is a gradual
increment in the relative density, which has also influenced the me­
chanical behavior of the test specimens (see section 3.5). The value of
the relative density increased from 95.78 % to 97.58 % for the 2.50
Mechanical properties were obtained from the tensile tests and
compared with those of the A360.0 die-cast alloy [42] (see Fig. 13). The
ultimate tensile strength (UTS) from 188.4 to 364.0 MPa, yield strength
from 106.8 to 200.1 MPa, and elongation ranging from 3.55 to 12.04 %
were obtained. The AlSi10Mg thin-walled specimens are comparable to
the cast AlSi10Mg material (A360.0) in terms of mechanical properties.
The strength and ductility are higher than those of A360.0 because the
thin-walled specimens were fabricated using the optimal process pa­
rameters [28] and the relative density is greater than 93 % and nearly
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Journal of Manufacturing Processes 66 (2021) 269–280
Fig. 11. Optical Microscopic images of the lateral face; (a-b) 2.50 mm specimen, (c-d) 3.50 mm specimen, (e-f) 5.0 mm specimen.
gradual increment from 192.50 to 227.90 MPa in UTS was found for the
1.50 ~ 2.0 mm specimens respectively (see Fig. 13). The UTS for the 3.0
and 3.5-mm wall thickness specimens are nearly equivalent to the diecasted conventional A360.0 alloy. The larger the wall thickness of
specimens, the higher was the UTS. The maximum value of 364.0 MPa is
reached for the 5.0 mm specimen. The yield strength (YS) behavior is
also similar to the UTS, but the slight variation is observed in the 1.50
mm wall thickness specimen with a value of 109.3 MPa. This variation
would also be seen in the uncertainty or error bar of UTS and YS, which
showed a larger value than other specimens. This behavior is due to
some internal porosities in the sample, which may have caused by low
UTS and YS.
The breakage elongation behavior of the thin-walled specimens can
also be seen from Fig. 13. The breakage elongation for the 0.50 mm wall
thickness specimen is 5.31 %, which represents better ductile behavior
than some slight thicker specimens. The breakage elongation has a
random behavior until 3 mm wall thickness specimens. It can be
observed that the breakage elongation decreased from 0.50 to 0.80 mm
specimens, then was increased till 1 mm specimen, and then a slight
drop to its minimum value of 3.76 % for 1.50 mm wall thickness spec­
imen. There are also some small variations in elongation that are
observed from 1.80 to 2.0 mm wall thickness specimen as shown in
Fig. 13. The increment in elongation remains continued and reached to
Fig. 12. The relative density of thin-walled specimens at actual wall thickness.
equal to 100 % for some specimens.
The UTS of 247.3 MPa was observed for 0.50 mm specimen, which
was decreased to 190.4 MPa for 1.20 mm specimen. Furthermore, the
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Journal of Manufacturing Processes 66 (2021) 269–280
Fig. 13. Mechanical properties of AlSi10Mg thin-walled specimens and comparison with A360.0.
the maximum value of 12.04 % for the 5.0 mm wall thickness specimen.
For all the wall thicknesses specimens, a comprehensive behavior is
also shown in Fig. 13, which shows mechanical strength performance
from 0.50 mm to 5.0 mm wall thickness specimens. It can also be
observed that the elongation at yield has nearly the identical values of
approximately 1.6 % for all the thin-walled specimens with the different
values of YS, which means that the elongation behavior at yield is
similar for the all wall thicknesses specimens. However, elongation at
breakage was different for all the wall thicknesses. The value of
breakage elongation for the 5.0 mm test specimens was higher than the
previous studies [1,33].
Fig. 14 shows the SEM images of fracture behavior of different thinwalled tensile deformation specimens. It can be observed that all thinwalled specimens are broken within the gauge length, which means
that there is an excellent strength of the specimens and stress concen­
tration towards the center of the specimens. Upon the observation of the
fracture surface, it is illustrated that there are porosities within the
specimens, which creates cracks for rupture behavior in tensile speci­
mens during the deformation. Upon the visual and microscopic obser­
vations, it is concluded that there are large porosities and voids in the
low dense test specimens. The high tensile strength specimens have
broken from the center of the gauge length.
Fig. 14. Fracture surfaces SEM images of thin-walled tensile specimens. a) 0.80 mm; (b) 1.20 mm; c) 2.0 mm; and d) 2.50 mm.
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Journal of Manufacturing Processes 66 (2021) 269–280
deviations at different wall thicknesses.
The development of porosities, voids, oxides particles, etc. are
observed in the OM images in the top and lateral surfaces of the polished
thin-walled specimens. From Figs. 7-11, it can be concluded that except
0.50 mm specimen, the thin-walled specimens till the 1.50 mm wall
thickness has more porosities in the specimens, which have been
developed due to the low interaction of the laser beam with the spec­
imen, low melting and cooling rate of powder particles and un-melted
powder particles. It is also revealed that more porosities have
appeared on the borderline of the specimens than the center region. The
thin-walled specimens with larger wall thickness have low porosities
which are attributed to proper melting and cooling of the powder
particles.
The relative densities of the thin-walled specimens show good and
fully dense behavior. The relative density is perfect for the 0.50 mm
specimen because of 50 % cross-section with border scans and the 0.80
mm specimen also obtained an excellent relative density. The relative
density decreases from 1.0 to 1.50 mm specimens which can also be seen
from the microscopic images (increment in porosities). It shows that the
lower relative density specimens have more porosities and voids than
the higher relative density specimens, which means that the porosity is
directly related to the relative density of the fabricated SLM compo­
nents. To attain maximum relative density and minimum porosity, each
powder particle during the layer must be fully melted and subsequently
welded together with the material solidified in the lower layer [16]. It is
concluded that the relative density behavior would be different at
various wall thicknesses. Hence, the factor of wall thickness could be
considered for better performance of the functional and the operational
components during the designing of SLMed parts.
The relative density has also influenced on the mechanical perfor­
mance of the SLM fabricated products. If the parts are not sufficiently
dense or more porosities are present in them, then the ability to bear
loads is reduced, and they suffer from good strength. All specimens have
observed good strength as compared to the cast Al-Si components [39].
Furthermore, some thin-walled specimens have low tensile strength,
especially 1 mm wall thickness specimen. The mechanical behavior of
different thin-walled specimens is compared with the relative density
which is shown in Fig. 16. From the previous discussion, it is concluded
that the mechanical strength is good as compared to casted specimens.
The higher strength and hardness in the cast components is achieved by
the establishment of Mg2Si precipitates during the heat treatment pro­
cess. For SLMed specimens, implicitly the higher strengths and hardness
are already obtained in the as-built condition, i.e. without heat treat­
ment [36].
From Fig. 16a, it can be observed that the tensile strength is
Fig. 14a shows the fractured image of 0.80 mm thickness tensile
specimen, which depicts the failure near the gauge line with porosities.
Similarly, porosities are also observed for 1.20 mm fracture tensile
specimen (see Fig. 14b) with different fracture patterns compared to that
of 0.80 mm specimen. For 2.0 mm and 2.50 mm tensile specimen frac­
ture, surface with porosities was the main cause of fracture at the
recorded tensile strength, as shown in Fig. 14c and d.
3.4. Micro hardness examination of different wall thicknesses
The Vickers microhardness of thin-walled specimens is shown in
Fig. 15, which shows a random behavior in comparison to the tensile
strength. The lowest value of 105.6 HV hardness is observed for the 0.80
mm wall thickness specimen and the highest value of 143.2 HV can be
seen for the 3.93 mm (4 mm) thin-walled specimen. The deviations and
uncertainty in the values were also shown in Fig. 15, and the uncertainty
was calculated by Eq. (7) for each test specimen. The maximum de­
viations were observed in 0.50 and 1.0 mm thin-walled specimens, and 6
mm bulk samples. The hardness behavior was also dependent on the
density of the fabricated SLM parts, which can be correlated. The values
of hardness are equivalent to or higher than the casted AlSi10Mg com­
ponents, which are also mentioned in Fig. 15 [39].
From Fig. 15, it can be observed that from 0.49 to 2.44 mm wall
thickness specimens, there is a very slight variation in the hardness
behavior. The considerable variation in hardness can be seen from 2.44
to 2.95 mm, corresponding hardness changes from 113.9 to 126.7 HV,
respectively. Thereafter, a high boost in hardness is observed from 127.3
to 143.2 HV for the corresponding wall thickness of 3.45–4 mm,
respectively. The bulk sample also demonstrated a good strength as
compared to high thickness specimens. It can be seen from Fig. 15 that
the hardness value is almost the same from 4.0 to 6.0 mm thickness
samples, but more deviations are observed in the bulk sample.
3.5. Relationship of OM images, UTS, YS, %age elongation, and microhardness with the relative density
The cast aluminum alloy AlSi10Mg is broadly used in the
manufacturing of AM products by SLM. It has been confirmed that the
thin-walled components with a minimum of 0.50 mm wall thickness can
be manufactured with fully dense and better strength. Porosity is an
issue during the fabrication of aluminum products by the SLM process.
The shrinkage of the wall thickness due to the fast melting and cooling
process and laser beam compensation parameters are observed in the
results. So, for the making of actual functional products, the shrinkage
allowance may be considered, which can be seen in Fig. 6 in the form of
Fig. 15. Micro Vickers hardness thin-walled test specimens in as-built conditions with the actual wall thickness.
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Journal of Manufacturing Processes 66 (2021) 269–280
Fig. 16. The relative density influence on the mechanical properties of SLM fabricated thin-walled specimens. a) UTS; b) 0.2 % offset YS; c) %age breakage
elongation; and d) Micro Vickers hardness.
4. Conclusions
increased by the increment in the relative density irrespective of the
0.50 mm and 0.80 mm wall thickness specimens, since these specimens
have almost higher values of relative density than any other thin-walled
specimen, but low strength due to the small size or overall volume of the
specimens. The tensile strength is also dependent on the porosities
presence in the specimens as shown in Fig. 16a, 93.6 % relative density
specimen (1.50 mm wall thickness) also has low strength due to the
presence of porosities as shown in Fig. 8. The YS behavior in comparison
with the relative density is similar to the UTS, and for the 1.0 mm test
specimen, the YS is lower as compared to other test specimens. The small
wall thickness specimens are also highlighted in Fig. 16b by circular
clouds.
The comparison of breakage elongation with the relative density is
shown in Fig. 16c, which also has a similar behavior pattern of strength.
The highest elongation of 12.04 % is achieved for the 5.0 mm wall
thickness sample. Therefore, good results for the strength and loadbearing abilities of SLM fabricated thin-walled, and lightweight speci­
mens are reported in the present work. Moreover, the overall strength
behavior is perfect for thin-walled specimens, and the tested wall
thicknesses may be applied in practical applications.
The hardness behavior is also compared to the relative density as
shown in Fig. 16d. The hardness behavior changes for different wall
thickness but behaves in the same manner as for the strength. The main
variation is found for the 93 % relative density specimen, which has a
suitable hardness as compared to the 95 % relative density specimens.
These variations are due to the fine grain structure and good bonding of
those specimens and also the location of the indentation. The hardness
values are also measured higher than the casted aluminum parts.
The higher strength and hardness values are attributed to the higher
relative density. The above analysis of relative density to the mechanical
properties is achieved because the relative density is directly related to
the wall thickness of the thin-walled specimens which have influenced
the strength of the specimens. The fracture behavior of the tensile
specimen showed that the excellent strength of the specimens. The
rupture was created due to the porosities in the test specimens.
The following points are concluded from the presented study on thinwalled parts of AlSi10Mg alloy:
• The different wall thickness thin-walled specimens are manufactured
in excellent conditions without any cracks, but little deformations.
The minimum deviation is 0.25 % for the 0.80 mm wall thickness,
and a maximum deviation of 5.5 % is for the 1.2 mm. The deviation
decreases as the wall thickness increases due to the shrinkage
behavior of aluminum alloys during the rapid melting and solidifi­
cation of the SLM process.
• The highest relative density of 99.86 % is attained for the 0.50 mm
thin-walled specimens, while the lowest relative density of 93.6 %
for the 1.50 mm test specimen.
• The OM images exhibited more porosities, and voids for the lowdensity test specimens. The lower densities and higher porosities
are formed because of the poor melting and cooling of the powder
particles.
• The mechanical performance behavior of thin-walled specimens is
also good in comparison to the conventional cast alloy. The higher
values of 250.9 MPa of tensile strength, 143.7 MPa of YS, and 5.31 %
of elongation were achieved by tensile testing of 0.50 mm thinwalled specimens. The maximum value of 364 MPa of UTS, 200.1
MPa of YS, and 12.04 % of elongation were attained for the 5.0 mm
wall thickness specimen.
• Hardness behavior is related to the relative density and wall thick­
ness. The maximum hardness of 143.2 HV for the 4.0 mm test
specimen and a minimum value of 105.6 HV for the 0.80 mm spec­
imen is reported.
• The current research has reported that a thin-walled of 0.50 mm wall
thickness could be manufactured for AlSi10Mg by using the SLM
process with minimum deviations, the higher values of densities, and
mechanical properties. The mechanical performance is related to the
wall thickness and the relative density of the thin-walled specimens.
If the value is high, then strength is also higher and if the relative
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Journal of Manufacturing Processes 66 (2021) 269–280
density is low then most probably the strength is even lower. The
porosities have also played a vital role in the strength and durability
of the thin-walled specimens.
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Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgments
This research is supported by the Natural Science Foundation of
Zhejiang Province (No. LY19E050019) and Natural Science Basic
Research Program of Shaanxi (Program No. 2020JQ-380, 2021JM-166,
2021JM-173).
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